A pair of surveys asked Americans a more concrete question: in 1960, whether they would be “displeased” if their child married someone outside their political party, and, in 2010, would be “upset” if their child married someone of the other party. In 1960, about 5 percent of Americans expressed a negative reaction to party intermarriage; in 2010, about 40 percent did (Republicans about 50 percent, Democrats about 30 percent).

A note of caution: This party animosity is not historically new, just new to last several decades. At least partisans today are not brawling with and killing one another, as was true in the 19th century. But something seems to have changed since the less polarized era of the mid-20th century.

This isn't surprising. I'd certainly be appalled if any child of mine married a Republican. But when pressed for the causes, the researchers jump to the conclusion that since American stances on the issues haven't changed much in the last 50 years, and since many Americans cannot reliably state which Party holds what positions on issues, that the entire problem lies with a fragmented media environment and negative advertising.

But that would be vastly underselling the cultural dynamics at play. There was something crucial that changed all of American politics after 1960: the Civil Rights Movement. The Civil Rights Movement and its aftershocks had a dramatic impact on the country that would not be reflected in most issues polling. One of those impacts was on political partisanship. I've noted in the past that it was largely the impact of the Civil Rights Movement (combined with the power of big money to lobby the racist vote) that gradually killed bipartisanship in the United States:

But by far the biggest is that the bipartisanship of the mid-20th century was a special artifact of the uneasy alliance between traditional urban liberal tribes and religious Dixiecratic populists in the South and Midwest. As I've written before, FDR was quite able to aggressively take on the financial and corporate interests of his time with a broad coalition. But he couldn't pass an anti-lynching law without destroying his support base, and he was all too willing to institute the Japanese internment camps. In other words, FDR could take on the power of big money with ease, but he couldn't take on the power of Big Racism.

The result of this dynamic was an uneasy bipartisanship between otherwise competing interests. Men like Strom Thurmond would vote for "socialist" policies as long as only whites got the benefits.

The advent of the Civil Rights movement marked the beginning of the end of bipartisanship. As tax dollars were increasingly seen as going toward non-whites, Dixiecrats became Republicans and allies of big business interests. Similar dynamics occurred with anti-Hispanic sentiment in the West. All the religious fervor that had been reserved for progressive social justice issues by the "Progressive" movement in the late 19th century (which included, by the way, quite conservative ideas like the prohibition of alcohol: late 19th century progressives would have strongly opposed modern liberals on issues like marijuana legalization alone...) flipped to socially conservative issues. The women's equality movement only added further fuel to the socially conservative patriarchal fire.

At this point it was easy and natural for the racist culture warriors to align completely with the corporatists. The need for uneasy alliances disappeared. The rationale for men like Strom Thurmond to support New Deal policies and chat about them at cozy cocktail parties disappeared. The battle lines were set.

I'm sure the fractured media environment is partly to blame for the increased partisan fervor. But that's not all. It's also a largely cultural phenomenon driven by a difference between the legacy of those who favor expanded rights for women and minorities, and those who don't. That in turn affects cultural issues of urbanism versus suburbanism and a host of other touchstones that are merely reflections of that same divide, but wouldn't show up on most issues-based polling that is the bread and butter of political scientists and media analysts.

Increased partisan fervor, in other words, is a real cultural phenomenon, not a media-driven tribal epiphenomenon. But to call out why that is would be hurtful to some people's feelings and cultural heritage, and thus cannot be said in polite discourse.